The Location Service (LCS) in a mobile communication network obtains the location information of a target User Equipment (UE) through a specific location technology. The location information may be longitude and latitude information, or the location of a local street. The location information may be sent to the target UE for locating the user, or sent to the communication system for area-based charging, or sent to an operator for operation and maintenance, or sent to other organizations or individuals who request to obtain the location of the user for the purpose of value-added services. The LCS is primarily applied to: emergency rescue, vehicle navigation, intelligent traffic system, work scheduling, team management, mobile yellow page query, and network performance enhancement.
The Open Mobile Alliance (OMA) has formulated many application-layer protocols with respect to LCS. The Secure User-Plane Location (SUPL) protocol is a location protocol specific to a SUPL Enabled Terminal (SET).
The process in the SUPL is categorized into Network Initiated (NI) process and SET Initiated (SI) process, depending on the initiator, where the NI process enables the network to locate the SET, and the SI process enables the SET to locate itself.
The User-plane Location Protocol (ULP) of the OMA defines a SUPL Location Platform (SLP). The SLP includes a SUPL Location Center (SLC) and a SUPL Positioning Center (SPC). The SLC is responsible for handling SUPL operations in the network on the user-plane bearer, and communications between SETs. The SPC is responsible for providing auxiliary data and handling location messages and processes.
For both the NI SUPL process and the SI SUPL process, the SLP server and the SET store all the current location trigger information. If the location trigger information on the SET is not synchronous with that on the SLP for certain reasons (for example, the user identity bound to the SET is changed, possibly because the user uses a different Subscriber Identity Module (SIM) or changes the SET, or the location trigger information on the SET is lost), the subsequent location process does not go on normally.
As an organization for formulating radio specifications of GSM networks and WCDMA networks, the 3rd Generation Partnership Project (3GPP) has formulated numerous protocols about the location service. Such protocols define the capabilities of the network in locating a SET, including: instant location, deferred location, and periodical location.
For deferred location, the location result is not necessarily returned to the location requester immediately; instead, the location process is triggered through an event (namely, time, or a specific radio network event) to obtain the location result finally. The triggering of the location process through an event is sometimes detected by the radio network, and is sometimes detected through the SET. Generally, several processes such as event delivery, event occurrence, and location trigger request are involved. The deferred location usually requires the SET to store some event information for triggering location, and relevant auxiliary information such as area information in the area triggering and time information in the periodical triggering.
Likewise, the location trigger information such as the area change event and the area information is stored in the SET. The SET relies on such information to judge whether the location needs to be reported. Once the SET loses such trigger information for certain reasons, the information on the SET is out of sync with the trigger information stored on the network-side device, which makes it impossible to report the deferred location of area change subsequently. Moreover, the request for deferred location of area change is specific to a particular user rather than SET hardware. Once the identity of the SET user is changed (for example, the user changes the SIM card or SET), the existing location of the user may not be handled normally.